1. Technical Field
This invention relates to scanning measurement systems which scan an object linearly and rotationally, particularly to optical scanning measurement systems, and in certain embodiments, to interferometric scanning measurement systems.
2. Description of Related Art
In many fields of manufacturing, the level of precision to which products can be made is continually advancing. There are many products which are axially symmetric, or nearly so, and which are made to exacting standards due to the particular applications of the products. Additionally, these axially symmetric products may be comprised of multiple layers or thin films of varying thicknesses and physical properties.
One example of such a product is the balloon catheter, which is used in balloon angioplasty medical procedures to open sclerotic arteries. Not surprisingly, in order to be safe and effective in such a procedure, a balloon catheter must satisfy a broad range of specifications. This is needed in order to obtain FDA approval for the catheter device and for operation of the catheter device manufacturing plant, as well as to minimize product liability of the manufacturing company. Wall thickness specifications for a balloon catheter are particularly important.
Whenever there is a product specification, there is a need to measure the product to confirm that it is meeting the specification. For an invasive medical device such as a balloon catheter, where a patient's life is at risk in the event of a product failure, it is required that every individual catheter be measured to determine that it meets specifications. It is undesirable that a sample of a production lot of catheters be measured, and then the full lot be deemed satisfactory. Thus, any measurement of catheter properties must be non-destructive and non-contact. Additionally, the measurement itself must be sufficiently reliable so as to have substantially no risk of mistakenly finding a defective catheter to be within specifications and releasing it for use in a patient, when it should be rejected and discarded. The measurement must also be sufficiently fast so as to enable the desired manufacturing throughput, in order for the overall catheter manufacturing process to be economically viable.
Scanning methods and apparatus which use an optical probe may be particularly effective in making wall thickness, diameter, and length measurements of balloon catheters, as well as various other high precision and/or multilayer axially symmetric products. Optical probe-based measurements are non-destructive, non-contact, highly precise, and fast. One particular optical probe-based measurement uses the principles of low coherence interferometry, wherein an optical probe directs low coherence light through a transparent, translucent or colored object. Reflected light is received back by the probe and transmitted to a signal converter and a computer. Software programs in the computer analyze the reflected light signals and determine dimensional and layer thickness(es) of the object. For further details on this measurement apparatus and methods, one may refer to U.S. Pat. Nos. 5,596,409, 5,659,392, 6,034,772, 6,034,774, 6,038,027, 6,067,161, 6,522,410, 6,724,487, all of Marcus et al.; and U.S. Pat. No. 7,206,076 of Blalock. The disclosures of these United States patents are incorporated herein by reference in their entireties.
A measurement product which employs low coherence interferometry is the OptiGauge™, which is manufactured and sold by Lumetrics, Inc. of West Henrietta, N.Y. This product meets the non-destructive, non-contact, and precision requirements for making measurements of balloon catheters and other similar high precision products made according to stringent specifications. Such capabilities notwithstanding, there has remained a need for an optical probe-based measurement system, whether it uses an interferometric probe, or another optical probe, wherein the system can perform a full scan along the length and around the circumference of an axially symmetric product. There is a need for such a system to have the capability to scan a product which has variation in diameter along its length. For balloon catheters and other objects having an internal cavity and a flexible wall, there is a need to stabilize the position of the flexible wall surface while making the measurements.
There is a further need for a system which can be programmed to perform an entire scan of the product automatically according to a computer program, acquire the thickness and diameter data of an array of axial and circumferential locations along the product, compare the data to product specifications, and to indicate whether the product is acceptable or rejected.